Based on the foregoing physiology, and testosterone's ability to rescue hypo-somatotropism in older men (Gentili et al 2000), we postulate that testosterone can (a) enhance endogenous GHRH secretion and/or (b) facilitate somatotrope responsiveness to GHRH. To this end, we are carrying out clinical experiments to drive the GHRHergic signalling pathway in older men while simultaneously fixing inputs by SS and GHRP before and after testosterone supplementation.